Depending on a patient's malocclusion, a variety of orthodontic treatments is available. In some of these treatments, extraction of teeth may be required in order to create space for the remaining teeth. In some treatments, a distalizing element may be used, possibly in combination with the extraction of one or more teeth.
A particular distalizing element is known from e.g. EP 1 433 435 and EP 1 649 824. These distalizers are especially adapted for the segmental distalization of the canine-to-molar posterior maxillary area. The distalizers of these documents comprise a mesial element which may be fixed by its base to an upper canine, and further comprises a distal element which may be fixed by its base to an upper molar, in particular the first molar.
The mesial element in these designs comprises both a base, and an arm that connects it to the distal element. The arm may be substantially arch shaped and may comprise a ball member at one of its ends. This ball member is received in a receptacle of the distal element that has a complementary shape to the ball member.
The mesial element may comprise a blunt projection that extends substantially forwards which may serve as a hooking element. In use, a bracket with a hook may be attached to a mandibular molar and an (orthodontic) rubber band may be suspended around this hook and the hooking element on the mesial element.
This way, a force pulling the maxillary canine backwards is provided. If the patient is wearing e.g. a splint (or another fixation device) that acts as a solid anchor and fixes the teeth of the mandible in position, it may be ensured that the teeth in the mandible do not move forwards, and that the maxillary canine is pulled backwards.
Due to the connection between the mesial element and the distal element of the distalizer, the maxillary molar may thus also be pushed backwards. At the same time, due to the shape of the arm in between the canine and the molar and due to the position of the distal element on the molar, a rotational force is also exerted upon the molar. This rotational force may result in a pivot about the palatal root of the maxillary molar. Also, a rotation in the distal direction of the molar (“uprighting”) may result. Thus a backwards force and a rotational force may be exerted upon the molar at the same time.
In order to avoid that the maxillary molar rotates too much in the distal direction (i.e. in this case, it would assume an orientation in which it is tilted backwards), the shape of the receptacle and the ball member are such that with a predetermined rotation of the ball member with respect to the upper molar, the ball member touches the inside of the receptacle and cannot rotate further. To this end, both the mesial element and distal element are mounted at the right height on the molar and canine and are mounted substantially straight along the locally defined mandible-maxilla (straight up-down) direction on the surface of the tooth. The arm is provided at a predefined angle with respect to the ball element. When both the canine and molar are actually straight, this angle will make sure that the ball member touches the border of the receptacle and cannot rotate further.
Similarly, the shape of the ball member and the border of the receptacle may be such that a rotation of the upper molar around its palatal root may be limited. Once a predetermined rotation is reached, the ball member may touch the border of the receptacle and not be able to rotate further.
It may thus be ensured that a distalization of the canine-molar segment may be combined with a proper (re)orientation of the set of teeth in the maxillary posterior region.
It is thus important that the ball member fits well in the receptacle of the distal segment.
It is furthermore important that the ball member once inserted in the receptacle stays in the receptacle and cannot slip out.
In the prior art, the method of assembling the distalizer comprises providing both the distal element and the mesial element of the distalizer, the arm connecting both elements being integrally formed with the mesial element. A receptacle is foreseen in the distal element and the receptacle comprises an opening for the introduction of the ball member at the end of the arm.
The ball element is slightly larger than the opening of the receptacle. The ball element is pushed into the receptacle. Upon introduction, the ball element and the border of the receptacle experience some deformation so that the ball is able to enter into the receptacle. This deformation may be mostly elastic, but the ball element could be slightly damaged. Given the importance of the ball element in the functioning of the distalizer, it is very important that the dimensions of the ball element and receptacle are well defined. The forced introduction of the ball element in the receptacle may thus cause a problem.
Additionally, it is possible for the ball element to slip out of the receptacle.
U.S. Pat. No. 5,620,321 discloses a telescoping mandibular device. The appliance comprises a pair of telescoping devices that attach on one end to the maxillary arch via a modified ball and socket device and on the other end to the mandibular arch via a modified ball and socket device. During assembly of the appliance in the mouth of the patient, after introduction of a ball in the mandibular socket, pliers may be used to plastically deform the mandibular socket legs.
U.S. Pat. No. 5,120,218 discloses an orthodontic traction device comprising a connection member and two attachment members. An attachment member may be produced with a slot that is transversely enlarged to be of approximately oval shape with its width at the minor axis just enough to permit the head of the pin to pass through it. Thereafter, with the pin in place the orthodontist applies the beak surface of a pair of jaws to the opposite sides of the device and squeezes to crimp the member and move the two sides toward one another until the jaw stop surfaces meet, when the sides of the slot will be parallel and able to retain the headed pin therein.
Both these prior art documents disclose the use of pliers (or similar) to apply force on both sides of an orthodontic device and deform it. Such a method of deformation is unsuitable for the distalizing element as herein described. The proper functioning of the distalizer is based on the collaboration between the surfaces of the ball member and the receptacle, which define collision points and upon which the distalizing effect is dependent. A proper treatment of a malocclusion with a distalizer would not be possible if either the ball member of the receptacle had an imperfection.
There thus exists a need to improve the method of manufacture and/or assembly of the distalizer that avoids or reduces these potential problems.